1. Field of the Invention
The present invention relates to a technology for optimizing the expenses of the image forming process related to multi-page copying.
2. Description of the Related Art
An image forming process in image forming apparatuses, such as electrophotographic type copiers, is performed in the following manner. A light source, such as a lamp, illuminates a surface of an original. Light reflected from the surface of the original is guided to the surface of a photosensitive drum to form thereon a latent image corresponding to the image on the surface of the original. A developing device then adheres toner to the latent image on the photosensitive drum to convert the latent image into a visible image (or a toner image). A transfer device then transfers the visible image to a paper and a fixing device fixes the toner image on the paper.
Some image forming apparatuses have a function of multi-page copying. Multi-page copying includes forming scaled-down images of a plurality of originals on a single sheet of paper. Multi-page copying is economical, because it reduces the usage of paper.
Some color digital copiers are equipped with an automatic document feeder (ADF). An automatic document feeder (ADF) includes a document tray, and when a stack of originals is set in the document tray, originals set in the document tray are fed one by one to the color digital copier. Some color digital copiers are equipped with an auto-color-selection function. By using the auto-color-selection function, color digital copiers can automatically determines whether an original is a color original or a black-and-white original. In color digital copiers that are equipped with both the ADF and the auto-color-selection function, users merely need to set a mixed lot of color and black-and-white originals in the document tray of the ADF, and press a copy “start” button. The color digital copiers then perform appropriate processing depending on whether the original is a color document or black-and-white document.
Color printing is generally more expensive than black-and-white printing. The auto-color-selection function can be advantageous as the cost of printing will be commensurate with the type of processing selected according to the type of the original by the auto-color-selection function.
Color digital copiers also use great quantities of consumables and have very high running costs. Often users enter into a maintenance contract, and have to bear maintenance expenditure, which varies according to the print output. The maintenance expenditure also varies according to how much of the printing is to be done in color and how much in black-and-white.
The automatic black-and-white/color determination by the auto-color-selection function thus serves to assign rates according to the printing method selected based on whether the original is a color document or a black-and-white document in a mixed lot of originals.
A copying apparatus and a control method thereof are disclosed in Japanese Patent Application Laid-open No. 2003-244365. In the technology disclosed in Japanese Patent Application Laid-open No. 2003-244365, prior to starting a copying operation, the cost is calculated according to the number of pages to be output, whether it is going to be color or black-and-white output, and the paper size, the calculated cost is presented to the user, and the copying operation is performed only if the user gives a command. Different rates are set for a full color copy and a black-and-white copy. Similarly, in color digital copiers with two-tone copying functionality (such as producing copies in black and red) or single-tone copying functionality (for example, producing copies in a single color other than black such as red), different rates are set for two-tone copy and single-tone copy. In other words, the cost of single-tone copy such as black-and-white, single-tone (other than black) copy, and two-tone copy, which have less toner consumption, is set less than for full-color copy. However, auto-color-selection function can only recognize a black-and-white original and a color original, i.e., it can not differentiate between a color original, a two-tone original and, a single-tone (other than black) original. Therefore, when auto-color-selection function is selected, a two-tone original is treated as a color original, and the cost calculated will be according to a full-color rate. Thus, the cost calculated and presented to the user for the two-tone copy is erroneously high, even though the user has the option of whether or not to give the copy command. Further, if the auto-color-selection function is used in combination with multi-page copying when there is a mixed lot of black-and-white and color originals, color printing has to be initiated even if there is only one color original among the originals to be printed on a single sheet of paper. Barring the case where all the originals are in color, the calculated cost will always be higher than what should be. Faced with such a situation, some users do not mind the cost calculated based to full-color rate for the sake of image quality, while others prefer cost-saving.
A solution for the above problem is provided in Japanese Patent Application Laid-open No. 2004-214794. In the technology disclosed in Japanese Patent Application Laid-open No. 2004-214794, based on the determination result of the auto-color-selection function, copies of the originals of the same type are put together on a sheet of paper, thus producing copies of the black-and-white originals and the color originals on different sheets of paper. Thus, cost control is achieved by segregating black-and-white copying and color copying. However, in this case too, the auto-color-selection function can only recognize a black-and-white original and a color original, i.e., can not differentiate between a color original a two-tone original. Therefore, if there is a mixed lot of black-and-white originals and two-tone originals, the cost for the two-tone copy is calculated based on full-color rate, even if the copies of all the two-tone originals are made on a separate sheet of paper from the black-and-white ones.